Full data from the study will be submitted for presentation at a future scientific conference.

The Phase 3 clinical trial program for sofosbuvir includes two additional studies evaluating 12 and 16 weeks of therapy with sofosbuvir plus RBV in HCV genotype 2 and 3 infected patients. A fourth Phase 3 clinical trial is evaluating sofosbuvir combined with RBV and peg-IFN among patients with HCV genotypes 1, 4, 5 and 6. Pending the results, these studies will support initial regulatory filings in mid-2013 for an all-oral therapy with sofosbuvir plus RBV among genotype 2/3 treatment-naïve, treatment-experienced and interferon-intolerant patients, and for sofosbuvir in combination with RBV and peg-IFN among treatment-naïve patients with HCV genotypes 1, 4, 5 and 6.

About Sofosbuvir

Sofosbuvir (formerly referred to as GS-7977) is a once-daily nucleotide analog polymerase inhibitor for the treatment of HCV infection. Sofosbuvir is being evaluated as part of multiple therapeutic regimens, including the programs outlined above in combination with RBV and peg-IFN. Additionally, sofosbuvir is being studied as a once-daily fixed-dose combination containing sofosbuvir and the NS5A inhibitor GS-5885, with the added goal of creating a potent, tolerable and convenient all-oral treatment for genotype 1 infected HCV patients that may eliminate the need for interferon and/or RBV.

Sofosbuvir and GS-5885 are investigational products and their safety and efficacy have not yet been established.

About Gilead Sciences

Gilead Sciences is a biopharmaceutical company that discovers, develops and commercializes innovative therapeutics in areas of unmet medical need. The company’s mission is to advance the care of patients suffering from life-threatening diseases worldwide. Headquartered in Foster City, California, Gilead has operations in North America, Europe and Asia Pacific.

Forward-Looking Statement

This press release includes forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to risks, uncertainties and other factors, including the possibility that the proportion of patients who maintain a sustained virologic response with longer follow up will not be as favorable as the sustained virologic response rates reported in this press release and the possibility of unfavorable results from additional clinical trials involving sofosbuvir and the fixed-dose combination of sofosbuvir and GS-5885. As a result, sofosbuvir and GS-5885 as single agents or as a fixed-dose combination may never be successfully commercialized. Further, Gilead may make a strategic decision to discontinue development of the compounds or the fixed-dose combination regimen if, for example, Gilead believes commercialization will be difficult relative to other opportunities in its pipeline. These risks, uncertainties and other factors could cause actual results to differ materially from those referred to in the forward-looking statements. The reader is cautioned not to rely on these forward-looking statements. These and other risks are described in detail in Gilead’s Quarterly Report on Form 10-Q for the quarter ended September 30, 2012, as filed with the U.S. Securities and Exchange Commission. All forward-looking statements are based on information currently available to Gilead, and Gilead assumes no obligation to update any such forward-looking statements.